It might have to do with the channel data, but I'm not sure. Schedules Direct gives you a 7 day free trial (which is actually 21 days because Myth downloads the next 14 days of data). So I would just sign up and configure it. Then if it works, you can pay (now $20 for a whole year of service).
As for the PVR being plugged in, that probably will be problem, but I don't think it's causing this particular one...